1. Field of the Invention
The present invention relates to a vehicular lamp. More particularly, the present invention relates to a vehicular lamp that is used for a vehicle.
2. Description of Related Art
Conventionally, a cold cathode fluorescent lamp having a cathode, a gate, and an anode applies an acceleration voltage between the anode and the cathode and also applies an extraction voltage between the gate and the cathode, and thus discharges electrons from the cathode toward the anode and collides the discharged electron against a phosphor on the anode, in order to cause the phosphor to emit light is known as disclosed, for example, in Japanese Patent Laid-Open No. 2000-173445.
Moreover, a switching regulator is used as a power source for the cold cathode fluorescent lamp in some cases. The switching regulator turns on or off an electric current flowing into a primary coil of a transformer so as to flow an electric current into a secondary coil. Then, the switching regulator smoothes the current and supplies the smoothed current to a load. After that, the switching regulator detects the current flowing into the load and adjusts time turning on or off the current in the primary coil of the transformer in order to keep the current supplied to the load constant.
In the transformer of the switching regulator, the primary coil and the secondary coil are wound close to each other in order to raise power conversion efficiency in some cases. Therefore, the transformer has large parasitic capacitance between the primary coil and the secondary coil. In this way, as the current flowing into the primary coil is turned on or off, a high-frequency current based on the parasitic capacitance and a change of current in the primary coil flows into the secondary coil. Moreover, when the cold cathode fluorescent lamp is turned on, e.g., the voltage of several kilovolts is applied between the anode and the cathode so as to flow the current of several ten microamperes between the anode and the cathode. Since the current flowing into the cold cathode fluorescent lamp during turning on the cold cathode fluorescent lamp is relatively small compared with the voltage applied to the primary coil and the secondary coil, the high-frequency current generated by on and off of the current in the primary coil cannot be ignored compared with the current to be flowed into the cold cathode fluorescent lamp, in some cases. Therefore, there has been a problem that it is difficult to keep the current in the cold cathode fluorescent lamp a predetermined value.